Under normal operating and storage conditions, lubricants are subject to high temperatures and oxygen which leads to their oxidation and decomposition. Oxidation of lubricants causes the build-up of oil-soluble acids, lacquers and sludge which contribute to serious damage to engines and other lubricated systems. Varnish and lacquer deposits form on hot metal surfaces that are exposed to the lubricant. These deposits are further oxidized to hard carbonacious materials. Antioxidant additives for lubricants have been described as improving lubricant thermal and oxidative stability which thereby enhances the ability of the lubricant to resist oxidation.
Additionally, the metal parts of mechanical systems under heavy loads and working under high performance conditions such as high speeds and temperatures will deteriorate due to the frictional forces created by relatively moving and bearing metal surfaces. Often, lubricants for such operations, i.e. high performance lubricants, do not prevent wear of the metal and as a result the performance of the system is adversely affected. It is desirable to blend additive packages containing antiwear/antifriction additives with lubricants in order to prevent wear and increase the service and operating life of the machinery.
Zinc dithiophosphates are often described as having antioxidant and antiwear properties when used with various oleagenous compositions. However, zinc-containing additives are undesirable because of high costs associated with the production of zinc and undesirable environmental effects of zinc derivatives.
Organotin compounds are described as high temperature stabilizers in polyvinylchloride (PVC) plastics especially rigid PVC as high temperature stabilizers in Kirk-Othmer's Encyclopedia of Chemical Technology, Vol. 16, pp 573-579, John Wiley and Sons Publishers (1981).
In U.S. Pat. No. 4,551,258 to Ikeda et al, dated Nov. 5, 1985, grease compositions containing the reaction products of zinc dithiophosphates, phosphoric acid esters and organotin compounds are disclosed as additives for greases.